50 parts per billion (ppb) (Figs. 1C and 3C)
and growth rates exceeding 20 ppb per cen-
tury, as recorded in the EDC ice core (Figs. 1E
and 3E). We dub these pulse-like CO 2 release
events CDJ+. Using this definition, we identify
five CDJ+ (9e, 11a.2, 11a.3, 11a.4, and 11e) (Fig.
1B). The major CH 4 rises associated with CDJ+
indicate abrupt DO-like warming in the NH
directly linked to AMOC invigorations ( 6 , 17 ).
Direct evidence for such AMOC strengthening
comes from associated abrupt rises in SST in
the NH (Fig. 2, F to H) and increases of benthic
d^13 C values (Fig. 2I), indicative of the inflow of
NA deep-water masses at IODP site U1385.
These findings are consistent with the two
previously identified CDJ+ events during the
last deglaciation, at the onsets of the Bølling-
Allerød and Preboral periods ( 6 , 9 ).
The most pronounced CDJ+ (CDJ+ 9e) takes
place during early interglacial conditions, when
CO 2 values are already above 285 ppm, a level
that is higher than typical peak-CO 2 mole
fractions during interglacial conditions over
the past 800 ka ( 3 ). The time resolution for
CDJ+ 9e is better than 90 years and shows
an exceptionally fast CO 2 increase of ~10 ppm
per century, as measured on the two neigh-
boring ice samples (Fig. 3B). Accounting for
the smoothing of atmospheric signals by the
bubbleenclosureprocess,weestimateanorig-
inal rate of atmospheric CO 2 increase of 26.2 ±
17.6 ppm per century (Fig. 3B and table S1)
( 20 ), which provides a benchmark for the pos-
sible range and speed of positive carbon cycle
feedbacks connected to AMOC variations during
the deglaciation. This rate exceeds previous es-
timates of maximum preindustrial atmospheric
increase rates ( 31 ) by a factor of seven but is still
a factor of nine lower than recent anthropo-
genic growth rates over the past decade ( 32 ).
The CO 2 decrease after CDJ+ 9e shows that
natural processes during interglacial condi-
tions allowed for a sustained CO 2 removal
from the atmosphere estimated at ~2 ppm per
century for ~2 ka (Figs. 1B and 3B).
The second variety of CDJ occurs inde-
pendently from major responses in the EDC
CH 4 record(Fig.1,CandE)(seesupple-
mentary text section of the supplementary
materials) and is dubbed CDJ−.Weidentify
two CDJ−(10a and 11a.2), which share sim-
ilar characteristics with the two CDJ−events
associated with HS 1 during the last degla-
ciation (~16 ka BP) and HS 4 ( 6 , 12 , 13 ). We
speculate that CDJ−can be attributed to car-
bon cycle processes caused by AMOC weak-ening. Although direct AMOC records do not
yet exist for MIS 9e to 12a, abrupt decreases
of benthicd^13 C indicate intrusions of Ant-
arctic bottom water masses at IODP site
U1385 (Fig. 2I) likely due to AMOC weakening,
similar to what occurred during HS in the
last glacial period ( 14 , 15 ). Note that major HS
(HS 10.1 and 10.2) are identified in Fig. 2 by
the drop in alkenone saturation index (UK′ 37 )–
based SST (Fig. 2G) and the decrease in ben-
thicd^13 C (Fig. 2I) indicative of a reduced state
of the AMOC. Whereas CDJ−10a is likely re-
lated to carbon cycle responses to an AMOC
slowdown caused by massive ice discharge
during HS 10.1 (Fig. 2I), there exists only
ambiguous evidence for CDJ−11a.2 being
associated with freshwater forcing. Low CH 4
levels(Fig.2E)andcoldSSTintheNA(Fig.
2F) indicate stadial conditions in the NH as-
sociated with CDJ−11a.2. Given the relative
age uncertainties between our ice core and
independently dated records ( 33 , 34 ), thed^18 O
calcite record from Sanbao Cave (Fig. 2J) ( 35 )
indicates a major shift of the ITCZ that may be
associated with CDJ−11a.2 ( 18 , 36 ).
Most notably, the new CO 2 record reveals
the clearly distinguishable CDJ 11c (12.9 ±
2.7 ppm increase within 191 ± 123 years) (Fig.Nehrbass-Ahleset al.,Science 369 , 1000–1005 (2020) 21 August 2020 4of6
Fig. 3. Detailed view of the two varieties of CDJ.(AtoE) Identical to Fig. 1.
The black linear segments in (B) indicate first-order approximations of the
atmospheric CO 2 evolution. The blue segment highlights the actual CDJ event.
These approximations for the atmospheric trajectories are optimized so that the
CO 2 curve after smoothing by the bubble enclosure process (gray lines) fits the
ice core data (red dots) best. The firn smoothing is realized by applying
improved gas enclosure characteristics for the EDC ice core ( 20 ). See table S1
for details. All remaining CDJ are shown in fig. S1.RESEARCH | REPORT